Impacts of prolonged power interruption on methane production in MEC-AD systems: Processes and mechanisms

Microbial electrolysis cell-assisted anaerobic digestion (MEC-AD) system has been recognized as an efficient method to promote the efficiency of the sludge resource recovery efficiency. In this study, the effects of the power-off duration intervals on the system are the focus. The results demonstrate that prolonging the power-off duration enhance methane production in the system. Compared to the short power-off intermittent mode (1d-on/1d-off), the extended power-off modes of 1d-on/5d-off and 1d-on/11d-off increase methane yields by 22.7 % and 7.2 %, respectively. Furthermore, the energy efficiency is substantially increased to 1102 % and 645 %. Mechanistic analysis reveals that extending the power-off duration enhances the bioconversion processes of organic matter in the system, including hydrolysis, acidogenesis, and methanogenesis, by upregulating the activities of key enzymes. Protease activity is increased by 17 % and 3 %, and coenzyme F420 activity is increased by 25 % and 14 %, respectively. A greater proportion of carbon in the sludge is directed toward methane production rather than carbon dioxide emission, resulting in enhanced removal efficiency of solid organic matter. Volatile suspended solids (VSS) removal reaches 63.5 % and 60.6 % for 1d-on/5d-off and 1d-on/11d-off modes, which is 114 % and 105 % higher than 24 h-on mode. MEC-AD operating under 1d-on/5d-off mode demonstrates superior performances, exhibiting enhanced electrochemical activity, elevated conductivity, promoted sludge aggregation, reduced extracellular polymeric substance (EPS) secretion, and increased Zeta potential. This study provides a cost-effective and superior approach to further improve sludge treatment efficiency, with implications for optimizing bioelectrochemical systems in resource recovery applications.